Antenna structures are used by cellular communications network/service providers to receive antennas for transmission and reception of radio signals. A typical antenna structure comprises a tower, one or more antenna brackets attached on the tower top, so that one or more antennas are attached on the antenna brackets. Usually, the tower is firstly assembled at the point of installation and then the antenna brackets are mounted on the tower itself. Antennas are attached to the antenna brackets by means of mounting bolts and screws or other securing means, defining a specific horizontal (azimuth) and vertical (tilt) directionality for the transmission and reception of radio signals.
To achieve high network performance, provide high quality radio link transmissions and receptions and ensure high spectrum efficiency, the panel antennas must be aligned with minimum inaccuracy (less than ±1°) to the specified horizontal (azimuth) and vertical (tilt) directionality angles provided by the radio planning process and antenna installation work orders. Accurate alignment of panel antennas is of paramount importance in a competitive wireless communication industry as even small errors in azimuth and tilt alignment (more than ±5° for azimuth and more than ±1° for tilt) can seriously degrade radio network quality. See, for example, the reference paper “Impact of Mechanical Antenna Downtilt on Performance of WCDMA Cellular Network” and also the paper “Impacts of Antenna Azimuth and Tilt Installation Accuracy on UMTS Network Performance” by Bechtel Corp.
Several prior art solutions are currently available for accurate alignment of antennas azimuth and tilt. For example, US20090021447 and US20110225804 describe a device for measuring the orientation of an antenna in three directions, i.e. azimuth, tilt and roll. The device is directly secured to an antenna and displays the measured values for azimuth, tilt and roll, allowing a user to accurately align an antenna to the desired directions. A deficiency of the prior art is that such a device cannot be employed in antenna structures having one or more antennas covered under a radome, due to the fact that antenna accessibility from an antenna technician, rigger or climber is not possible or generally limited (examples of such antenna structures are disclosed in US20050134512A1 & WO2011042226). As a result, the use of the measurement devices described in US20090021447 and US20110225804 are not applicable to serve the purpose of accurate alignment of antenna structures covered under a radome.
Furthermore, due to modern networks' dynamic nature, continuous antenna azimuth and tilt re-adjustment during the lifecycle of a base station site (for one or more antennas) is required; therefore, the antenna brackets, the antennas or the antenna structure itself should be capable to provide the suitable means for facilitating such needs. Each antenna is designed to serve a specific area, namely a cell or sector. Cell direction, i.e. antenna azimuth & tilt, is produced by modeling multiple aspects of radio access technology as well as accounting for radio propagation science by using radio planning tools. The main aim of the radio network planning process is to provide optimum performance for the radio network in terms of coverage, capacity and quality. The network planning process and base station site design criteria vary from cluster to cluster depending upon the dominating factor, which is optimum performance. Said coverage may include defining the coverage areas, service probability and related signal strength; said capacity may include subscriber density and traffic profiles in the coverage region and whole area, availability of the frequency bands, frequency planning methods, and other information such as guard band and frequency band division; said quality is related to radio interference metrics such as signal to noise ratio. Since all radio network performance aspects are fully dynamic, the radio network planning process that selects antenna directionality at installation phase cannot ensure that the selection criteria (i.e. capacity, coverage and quality) will remain the same after a period of time. Usually, the antennas are installed and operated for at least 7 to 10 years or even more. This fact by itself, means that the antenna azimuth and tilt directions must often change during the base station site lifecycle by re-adjustment means. Ideally, antenna azimuth and tilt re-adjustment should be considered at least once every six months for every antenna in the network, especially in urban and heavy urban areas where the demands on capacity and quality of radio base station clusters are continuously shifting.
When antenna system azimuth and tilt re-adjustment is to be performed, such re-adjustment should take place without the need to climb on the tower top, so as to avoid complicated operations of high opex (operational expediture) costs (due to climbing) and also ensuring health and safety at work for antenna technicians, riggers and climbers. It is well known that human exposure on high electromagnetic fields is an issue to be considered by the network service providers for those working in close proximity to radiating antenna systems. Climbing on the tower top in order to set or re-adjust the directionality of antennas is not avoided by use of the devices disclosed in US20090021447 and US20110225804 as they do not provide the means for such operations. However, when such devices are not used, the problem of antennas azimuth and tilt accurate alignment for any directionality re-adjustment by remote operation remains.
In the case where there is a need to satisfy both antenna alignment accuracy and remote re-adjustability (with no climbing) with accuracy, an electromechanical apparatus that performs both actions needs to be deployed. A single pivot axis antenna bracket that offers remote azimuth adjustment by electromechanical means is disclosed in WO2007093689A1. However, a deficiency of such prior art is that such an antenna bracket cannot satisfy the alignment accuracy required by the radio planning process and antenna system installation work orders without use of devices disclosed in US20090021447 and US20110225804. This is due to the fact that the proposed electromechanical system attached on the antenna bracket does not provide absolute azimuth, tilt and roll measurement means. The result of this is that all of the disadvantages introduced by use of US20090021447 and US20110225804 (as described in the previous paragraphs) follow as disadvantages also for apparatus of WO2007093689A1. Furthermore, a single pivot axis antenna system that offers remote azimuth adjustment by electromechanical actuation but also attempts to provide absolute azimuth, tilt and roll measurement means is also disclosed on US20090195467. However, a deficiency of such prior art is that such a solution utilizes an earth gravitational magnetic field sensor which, by default, introduces inaccuracy due to magnetic field disturbances caused from the antenna systems, the antenna brackets and the antenna structure itself (i.e. soft and hard iron effects). Therefore, such a solution, although it offers both antenna system alignment accuracy and remote re-adjustability with accuracy, does not address the issue of high overall accuracy.
The deficiencies exemplary of the apparatus of WO2007093689A1 and US20090195467 are applicable not only in these documents, but also when antenna systems are attached on antenna brackets that utilize more than one pivot axis for horizontal (azimuth) alignment and movement. In a particular example of antenna system directionality, two antennas may need to have the same horizontal direction or the same azimuth angle. In order to align and direct both antenna systems to the same azimuth angle, prior art US20060087476 proposes a dual pivot axis antenna bracket for installation on a triangular tower utilizing antenna sector frames. WO2011042226 (GB2474605) proposes a dual pivot axis antenna bracket for installation on a monopole structure by utilizing a collar. This prior art provides the capability, due to the dual pivot axis antenna bracket attached on the antenna structure, to offer full motion freedom on the antenna system(s) (needed for future horizontal azimuth re-adjustments) by maximizing the allowable antenna system horizontal (azimuth) movement range.
It is the purpose of the present invention to overcome or at least mitigate at least some of the aforementioned disadvantages of the prior art. In particular, it is the purpose of the present invention to propose a method for and apparatus for enabling the accurate, and repeatably accurate, alignment of communication antenna systems that are attached on either single or dual pivot axis antenna brackets, without the need for a technician, rigger or climber to come in direct contact with the antenna system itself.